Method for producing dielectric film, method for producing piezoelectric element, method for producing liquid-jet head, dielectric film, piezoelectric element, and liquid-jet apparatus

ABSTRACT

A method for producing a dielectric film, comprising: a coating step of coating a colloidal solution containing an organometallic compound containing a metal constituting a dielectric film containing at least a lead component to form a dielectric precursor film; a drying step of drying the dielectric precursor film; a degreasing step of degreasing the dielectric precursor film; and a firing step of firing the dielectric precursor film to form a dielectric film, and wherein the drying step includes a first drying step of heating the dielectric precursor film to a temperature lower than the boiling point of a solvent, which is a main solvent of the material, and holding the dielectric precursor film at the temperature for a certain period of time to dry the dielectric precursor film, and a second drying step of drying the dielectric precursor film at a temperature in the range of 140° C., to 170° C., the degreasing step is performed at a degreasing temperature of 350° C. to 450° C. and at a heating-up rate of 15 [° C./sec] or higher, and the firing step is performed at a heating-up rate of 100 [° C./sec] to 150 [° C./sec].

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 11/392,757 filed Mar. 30,2006. Priority is claimed from JPA 2005-104517 filed Mar. 31, 2005, andalso from JPA 2006-056096 filed Mar. 2, 2006. The entire disclosures ofthe prior application, application Ser. No. 11/392,757, and theabove-identified priority documents, are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a dielectric film comprising a dielectricmaterial including a piezoelectric material, a piezoelectric element, aliquid-jet apparatus, a method for producing a dielectric film, a methodfor producing a piezoelectric element having a piezoelectric filmcomprising a piezoelectric material, and a method for producing aliquid-jet head.

2. Description of the Related Art

A piezoelectric element used in a liquid-jet head, etc. is an elementcomprising a piezoelectric film sandwiched between two electrodes, thepiezoelectric film comprising a piezoelectric material having anelectromechanical conversion function. The piezoelectric film iscomposed of, for example, a crystallized piezoelectric ceramic.

An example of a liquid-jet head using such a piezoelectric element is anink-jet recording head in which a portion of a pressure generatingchamber communicating with a nozzle orifice for ejection of ink dropletsis constituted of a vibration plate, and the vibration plate is deformedby the piezoelectric element to pressurize ink in the pressuregenerating chamber, thereby ejecting ink droplets from the nozzleorifice. Two types of ink-jet recording heads are put into practicaluse. One of them uses a piezoelectric actuator in a longitudinalvibration mode which expands and contracts in the axial direction of thepiezoelectric element. The other uses a piezoelectric actuator in aflexural vibration mode. As the ink-jet recording head using theactuator in the flexural vibration mode, there is known, for example, anink-jet recording head having a piezoelectric element which has beenformed by forming a uniform piezoelectric layer over the entire surfaceof the vibration plate by a film-forming technology, and cutting thepiezoelectric layer into forms corresponding to the pressure generatingchambers by lithography to form the piezoelectric element independentlyfor each pressure generating chamber.

The so-called sol-gel process is known as a method for producing thepiezoelectric layer constituting the piezoelectric element. According tothis method, a sol of an organometallic compound is coated on asubstrate having a lower electrode formed thereon, followed by dryingand gelling (degreasing) the coating to form a piezoelectric precursorfilm. This step of forming the precursor film is performed at leastonce. Then, the resulting precursor film is heat-treated at a hightemperature for crystallization. These steps are repeated a plurality oftimes to prepare a piezoelectric layer (piezoelectric thin film) of apredetermined thickness.

The so-called MOD (metal-organic decomposition) method is known asanother method for producing the piezoelectric layer constituting thepiezoelectric element. This method generally comprises dissolving anorganometallic compound, such as a metal alkoxide, in an alcohol, addinga hydrolysis inhibitor or the like to obtain a colloidal solution,coating the colloidal solution on a suitable material, then drying andfiring the coating to form the piezoelectric layer.

The conventional methods for producing the piezoelectric layer aredisclosed, for example, on Japanese Patent Application Laid-Open No.1997-223830 (pages 4 to 6) and Laid-Open No. 1994-005946. According tothese methods, a piezoelectric layer of 1 μm or more in thickness can beformed relatively satisfactorily, and the occurrence of cracks can beprevented. However, the methods pose the problems that the crystallinestate of the piezoelectric layer, such as the crystal grain size ororientation, is difficult to control, and a piezoelectric layer havingdesired characteristics is not obtained. Such problems are not limitedto the piezoelectric film comprising the piezoelectric material for usein the piezoelectric element, etc. of the liquid-jet head, but aresimilarly encountered with dielectric films comprising other dielectricmaterials.

SUMMARY OF THE INVENTION

The present invention has been accomplished in the light of theabove-mentioned circumstances. It is an object of the present inventionto provide a dielectric film whose crystalline state is controlledrelatively easily and which gives constantly stable characteristics, amethod for producing the dielectric film, a method for producing apiezoelectric element, a method for producing a liquid-jet head capableof improving the characteristics of the piezoelectric element, and aliquid-jet apparatus.

A first aspect of the present invention for attaining the above objectis a method for producing a dielectric film, comprising: a coating stepof coating a colloidal solution containing an organometallic compoundcontaining a metal constituting a dielectric film containing at least alead component to form a dielectric precursor film; a drying step ofdrying the dielectric precursor film; a degreasing step of degreasingthe dielectric precursor film; and a firing step of firing thedielectric precursor film to form a dielectric film, and wherein thedrying step includes a first drying step of heating the dielectricprecursor film to a temperature lower than a boiling point of a solvent,which is a main solvent of the material, and holding the dielectricprecursor film at the temperature for a certain period of time to drythe dielectric precursor film, and a second drying step of drying thedielectric precursor film at a temperature in a range of 140° C. to 170°C., the degreasing step is performed at a degreasing temperature of 350°C. to 450° C. and at a heating-up rate of 15 [° C./sec] or higher, andthe firing step is performed at a heating-up rate of 100 [° C./sec] to150[° C./sec].

In the first aspect of the present invention, the drying step and thedegreasing step narrow the distribution of the composition ratios ofcomponents other than lead constituting the dielectric film, and thefiring step decreases foreign matter. As a result, crystals of thedielectric film can be grown satisfactorily, and the dielectric film inthe desired crystalline state can be formed. That is, the dielectricfilm having the proportions of the components at the B site distributeduniformly, and a small composition gradient is obtained.

A second aspect of the present invention is the method for producing adielectric film according to the first aspect, characterized in that thedielectric film containing at least the lead component is lead zirconatetitanate (PZT), and a distribution of a Zr/Ti composition in a filmthickness direction is rendered less than 3%, when expressed as a valueof a Zr/Ti composition gradient analyzed by ESCA, by the drying step,the degreasing step, and the firing step.

In the second aspect of the present invention, a dielectric film havingZr/Ti uniformly distributed therein is obtained.

A third aspect of the present invention is the method for producing adielectric film according to the first aspect, characterized in that thedielectric film containing at least the lead component is lead zirconatetitanate (PZT), and a composition of the colloidal solution is such thata ratio of Pb:(Zr/Ti) is (1.10-1.20):1.00, and a ratio of Zr:Ti is(0.46-0.51):(0.54-0.49).

In the third aspect of the present invention, the proportion of Pb isset, and the ratio of Zr:Ti is set, whereby the amount of displacementof the dielectric film can be ensured for a long term.

A fourth aspect of the present invention is the method for producing adielectric film according to the first aspect, characterized in that thedielectric film containing at least the lead component is lead zirconatetitanate (PZT), and a composition of the colloidal solution is such thata ratio of Pb:(Zr/Ti) is 1.18:1.00, and a ratio of Zr:Ti is(0.46-0.51):(0.54-0.49).

In the fourth aspect of the present invention, the ratio of Zr:Ti isset, whereby the amount of displacement of the dielectric film can beensured for a long term.

A fifth aspect of the present invention is the method for producing adielectric film according to the first aspect, characterized in that thedielectric film containing at least the lead component is lead zirconatetitanate (PZT), and a composition of the colloidal solution is such thata ratio of Pb:Zr:/Ti is 1.18:0.51-0.52:0.48-0.49.

In the fifth aspect of the present invention, the amount of displacementand durability of the dielectric film exist together at a high level,whereby the amount of displacement of the dielectric film can be ensuredfor a considerably long term.

A sixth aspect of the present invention is the method for producing adielectric film according to any one of the first to fifth aspects,characterized in that in the firing step, the dielectric precursor filmis heated by an RTA method.

In the sixth aspect of the present invention, the dielectric precursorfilm can be rapidly heated at a desired heating-up rate by the RTAmethod.

A seventh aspect of the present invention is the method for producing adielectric film according to any one of the first to sixth aspects,characterized in that crystals are preferred-oriented in a (100) planeof a rhombohedral system.

In the seventh aspect of the present invention, the orientation ofcrystals is controlled, whereby a dielectric film excellent inmechanical characteristics can be formed.

An eighth aspect of the present invention for attaining the above objectis a method for producing a piezoelectric element, comprising the stepsof: forming a lower electrode film on a substrate; forming apiezoelectric layer on the lower electrode film; and forming an upperelectrode film on the piezoelectric layer, and wherein the step offorming the piezoelectric layer is a method for producing the dielectricfilm produced by the producing method according to any one of the firstto seventh aspects.

In the eighth aspect of the present invention, crystals of thedielectric film grow satisfactorily, thus making it possible to obtain apiezoelectric element having a piezoelectric layer comprising adielectric film in a desired crystalline state.

A ninth aspect of the present invention for attaining the above objectis a method for producing a liquid-jet head, which uses thepiezoelectric element produced by the producing method according to theeighth aspect.

In the ninth aspect of the present invention, it is possible to obtain aliquid-jet head furnished with a piezoelectric element having apiezoelectric layer comprising a dielectric film in a desiredcrystalline state.

A tenth aspect of the present invention for attaining the above objectis a dielectric film in which a distribution of a Zr/Ti composition in afilm thickness direction of lead zirconate titanate (PZT) is renderedless than 3% when expressed as a value of a Zr/Ti composition gradientanalyzed by ESCA.

In the tenth aspect of the present invention, a dielectric film havingZr/Ti uniformly distributed therein is obtained.

An eleventh aspect of the present invention for attaining the aboveobject is a piezoelectric element comprising a lower electrode filmformed on a substrate, the dielectric film according to the tenth aspectprovided as a layer on the lower electrode film, and an upper electrodefilm formed on the dielectric film as the layer.

In the eleventh aspect of the present invention, a piezoelectric elementhaving, as a piezoelectric layer, a dielectric film having Zr/Tiuniformly distributed therein is obtained.

A twelfth aspect of the present invention for attaining the above objectis a liquid-jet apparatus including a liquid-jet head having thepiezoelectric element according to the eleventh aspect as a drive sourcefor ejecting liquid droplets through nozzle orifices.

In the twelfth aspect of the present invention, it is possible to obtaina liquid-jet apparatus furnished with a piezoelectric element having, asa piezoelectric layer, a dielectric film having Zr/Ti uniformlydistributed therein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptionsin conjunction with the accompanying drawings.

FIG. 1 is an exploded perspective view of a recording head according toEmbodiment 1.

FIGS. 2A and 2B are, respectively, a plan view and a sectional view ofthe recording head according to Embodiment 1.

FIGS. 3A to 3D are sectional views showing a manufacturing process forthe recording head according to Embodiment 1.

FIGS. 4A to 4C are sectional views showing the manufacturing process forthe recording head according to Embodiment 1.

FIG. 5 is a matrix diagram of degreasing conditions.

FIGS. 6A and 6B are views showing the depth profiles of piezoelectriclayers.

FIGS. 7A and 7B are TEM images showing the crystalline states of thepiezoelectric layers.

FIG. 8 is a tabular view illustrating the dependence of PZTcrystallinity on the degreasing conditions.

FIG. 9 is a graph showing the relationship between the PZT (100)half-width and temperature.

FIGS. 10A and 10B are TEM images showing the crystalline states of thepiezoelectric layers.

FIGS. 11A and 11B are TEM images showing the crystalline states of thepiezoelectric layers.

FIG. 12 is a view showing the depth profile of the piezoelectric layer.

FIG. 13 is a tabular view showing the results of improvement of heattreatment conditions.

FIG. 14 is a graph showing the PZT (100) diffraction peak.

FIGS. 15A to 15D are sectional views showing the manufacturing processfor the recording head according to Embodiment 1.

FIGS. 16A to 16C are sectional views showing the manufacturing processfor the recording head according to Embodiment 1.

FIG. 17 is a graph showing the relationship between the amount of Pb andthe decrease rate of displacement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail based on theembodiments offered below.

Embodiment 1

FIG. 1 is an exploded perspective view showing an ink-jet recording headaccording to Embodiment 1 of the present invention. FIG. 2A and FIG. 2Bare a plan view and a sectional view, respectively, of the ink-jetrecording head in FIG. 1. As illustrated in these drawings, apassage-forming substrate 10, in the present embodiment, consists of asingle crystal silicon substrate having a plane (110) of the planeorientation. A 0.5 to 2 μm thick elastic film 50, composed of silicondioxide formed beforehand by thermal oxidation, is formed on one surfaceof the passage-forming substrate 10. In the passage-forming substrate10, a plurality of pressure generating chambers 12 are arranged parallelin the width direction thereof. A communicating portion 13 is formed ina region of the passage-forming substrate 10 longitudinally outward ofthe pressure generating chambers 12, and the communicating portion 13and each pressure generating chamber 12 are brought into communicationvia an ink supply path 14 provided for each pressure generating chamber12. The communicating portion 13 communicates with a reservoir portionof a protective plate (to be described later) to constitute a reservoirserving as a common ink chamber for the respective pressure generatingchambers 12. The ink supply path 14 is formed in a smaller width thanthat of the pressure generating chamber 12 to keep constant the passageresistance of ink flowing from the communicating portion 13 into thepressure generating chamber 12.

Onto the opening surface of the passage-forming substrate 10, a nozzleplate 20 having nozzle orifices 21 bored therein is secured via anadhesive agent or a heat sealing film. The nozzle orifices 21communicate with near-end portions of the pressure generating chambers12 on the side opposite to the ink supply paths 14. The nozzle plate 20comprises a glass ceramic, a single crystal silicon substrate, orstainless steel having a thickness of, for example, 0.01 to 1 mm, and alinear expansion coefficient of, for example, 2.5 to 4.5 [×10⁻⁶/° C.] at300° C. or below.

On the side of the passage-forming substrate 10 opposite to its openingsurface, the elastic film 50 comprising silicon dioxide (SiO₂) andhaving a thickness, for example, of about 1.0 μm is formed, as describedabove. An insulation film 55 comprising zirconium oxide (ZrO₂) andhaving a thickness, for example, of about 0.4 μm is formed on theelastic film 50. On the insulation film 55, a lower electrode film 60with a thickness, for example, of about 0.2 μm, a piezoelectric layer 70with a thickness, for example, of about 1.0 μm, and an upper electrodefilm 80 with a thickness, for example, of about 0.05 μm are formed in alaminated state by a process (to be described later) to constitute apiezoelectric element 300. The piezoelectric element 300 refers to aportion including the lower electrode film 60, the piezoelectric layer70, and the upper electrode film 80. Generally, one of the electrodes ofthe piezoelectric element 300 is used as a common electrode, and theother electrode and the piezoelectric layer 70 are constructed for eachpressure generating chamber 12 by patterning. A portion, which iscomposed of any one of the electrodes and the piezoelectric layer 70that have been patterned, and which undergoes piezoelectric distortionupon application of voltage to both electrodes, is called apiezoelectric active portion. In the present embodiment, the lowerelectrode film 60 is used as the common electrode for the piezoelectricelements 300, while the upper electrode film 80 is used as an individualelectrode of each piezoelectric element 300. However, there is no harmin reversing their usages for the convenience of a drive circuit orwiring. In either case, it follows that the piezoelectric active portionis formed for each pressure generating chamber 12. Herein, thepiezoelectric element 300 and a vibration plate, where displacementoccurs by a drive of the piezoelectric element 300, are referred tocollectively as a piezoelectric actuator. A lead electrode 90comprising, for example, gold (Au) is connected to the upper electrodefilm 80 of each piezoelectric element 300. Voltage is appliedselectively to each piezoelectric element 300 via the lead electrode 90.

The material for the piezoelectric layer 70 constituting thepiezoelectric element 300 may be, for example, a ferroelectricpiezoelectric material such as lead zirconate titanate (PZT), or arelaxor ferroelectric having a metal, such as niobium, nickel,magnesium, bismuth or yttrium, added to such a ferroelectricpiezoelectric material. The composition of the piezoelectric layer 70may be chosen, as appropriate, in consideration of the characteristics,uses, etc. of the piezoelectric element 300. Its examples are PbTiO₃(PT), PbZrO₃ (PZ), Pb(Zr_(x)Ti_(1-x))O₃ (PZT),Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃ (PMN-PT), Pb(Zn_(1/3)Nb_(2/3))O₃—PbTi_(O3)(PZN-PT), Pb(Ni_(1/3)Nb_(2/3))O₃—PbTiO₃ (PNN-PT),Pb(In_(1/2)Nb_(1/2))O₃—PbTiO₃ (PIN-PT), Pb(Sc_(1/2)Ta_(1/2))O₃—PbTi_(O3)(PST-PT), Pb(Sc_(1/2)Nb_(1/2))O₃—PbTiO₃ (PSN-PT), BiScO₃—PbTiO₃ (BS-PT),and BiYbO₃—PbTiO₃ (BY-PT).

A protective plate 30 having a piezoelectric element holding portion 31,which can ensure in a region opposed to the piezoelectric elements 300such a space as not to impede the movement of the piezoelectric elements300, is joined onto a surface of the passage-forming substrate 10 wherethe piezoelectric elements 300 have been formed. Since the piezoelectricelements 300 are formed within the piezoelectric element holding portion31, they are protected in a state nearly free from the influence of anexternal environment. In the protective plate 30, a reservoir portion 32is provided in a region corresponding to the communicating portion 13 ofthe passage-forming substrate 10. The reservoir portion 32, in thepresent embodiment, is formed so as to penetrate the protective plate 30in its thickness direction and extend along the parallel arrangementdirection of the pressure generating chambers 12. The reservoir portion32, as described earlier, is brought into communication with thecommunicating portion 13 of the passage-forming substrate 10 toconstitute a reservoir 100 which serves as the common ink chamber forthe respective pressure generating chambers 12.

A through-hole 33, which penetrates the protective plate 30 in itsthickness direction, is provided in a region of the protective plate 30between the piezoelectric element holding portion 31 and the reservoirportion 32. Within the through-hole 33, a part of the lower electrodefilm 60 and a front end portion of the lead electrode 90 are exposed,and an end of connection wiring extending from a drive IC (not shown) isconnected to the lower electrode film 60 and the lead electrode 90.

The material for the protective plate 30 is, for example, glass, aceramic material, a metal, or a resin. More preferably, however, theprotective plate 30 is formed from a material having nearly the samethermal expansion coefficient as that of the material for thepassage-forming substrate 10. In the present embodiment, the protectiveplate 30 is formed using a single crystal silicon substrate which is thesame material as the material for the passage-forming substrate 10.

Furthermore, a compliance plate 40, which consists of a sealing film 41and a fixing plate 42, is joined onto the protective plate 30. Thesealing film 41 comprises a low rigidity, flexible material (forexample, a polyphenylene sulfide (PPS) film of 6 μm in thickness), andthe sealing film 41 seals one surface of the reservoir portion 32. Thefixing plate 42 is formed from a hard material such as a metal (forexample, stainless steel (SUS) of 30 □m in thickness). A region of thefixing plate 42 opposed to the reservoir 100 defines an opening portion43 completely deprived of the plate in the thickness direction. Thus,one surface of the reservoir 100 is sealed only with the sealing film 41having flexibility.

With the ink-jet recording head of the present embodiment describedabove, ink is taken in from an external ink supply means (not shown),and the interior of the head ranging from the reservoir 100 to thenozzle orifices 21 is filled with the ink. Then, according to recordingsignals from the drive IC (not shown), voltage is applied between thelower electrode film 60 and the upper electrode film 80 corresponding tothe pressure generating chamber 12 to flexibly deform the elastic film50, the insulation film 55, the lower electrode film 60 and thepiezoelectric layer 70. As a result, the pressure inside the pressuregenerating chamber 12 rises to eject ink droplets through the nozzleorifice 21.

The method for producing the above-described ink-jet recording head willbe described with reference to FIGS. 3A to 3D through FIGS. 4A to 4C.FIGS. 3A to 3D and 4A to 4C are sectional views in the longitudinaldirection of the pressure generating chamber 12. Firstly, as shown inFIG. 3A, a passage-forming substrate wafer 110, which is a siliconwafer, is thermally oxidized in a diffusion furnace at about 1,100° C.to form a silicon dioxide film 51 constituting the elastic film 50 onthe surface of the wafer 110. In the present embodiment, a silicon waferhaving a relatively large thickness of about 625 μm and having highrigidity is used as the passage-forming substrate 10.

Then, as shown in FIG. 3B, the insulation film 55 comprising zirconiumoxide is formed on the elastic film 50 (silicon dioxide film 51).Concretely, a zirconium layer is formed on the elastic film 50 by DCsputtering, and then the zirconium layer is thermally oxidized to formthe insulation film 55 comprising zirconium oxide. Then, as shown inFIG. 3C, platinum (Pt) and iridium (Ir), for example, are stacked on theinsulation film 55 to form the lower electrode film 60, whereafter thelower electrode film 60 is patterned into a predetermined shape.

Then, as shown in FIG. 3D, the piezoelectric layer 70 comprising, forexample, lead zirconate titanate (PZT) is formed. In the presentembodiment, a so-called sol comprising a metal organic materialdissolved or dispersed in a catalyst is coated and dried to be gelled,and is further fired at a high temperature to obtain the piezoelectriclayer 70 comprising a metal oxide. That is, the piezoelectric layer 70is formed by the sol-gel process.

The material for the piezoelectric layer 70 is not limited to leadzirconate titanate, and may be, for example, a piezoelectric materialother than relaxor ferroelectrics (for example, PMN-PT, PZN-PT, PNN-PT).The method for forming the piezoelectric layer 70 is not limited to thesol-gel process. For example, the MOD (metal-organic decomposition)method may be used.

A concrete procedure for forming the piezoelectric layer 70 begins withforming a piezoelectric precursor film 71, which is a PZT precursorfilm, on the lower electrode film 60, as shown in FIG. 4A. That is, asol (solution) containing a metal organic compound is coated on thepassage-forming substrate 10 on which the lower electrode film 60 hasbeen formed (a coating step). Then, the piezoelectric precursor film 71is heated from room temperature to a temperature lower than the boilingpoint of a solvent, which is a main solvent of the sol, and dried for acertain period of time to evaporate the solvent of the sol, therebydrying the piezoelectric precursor film 71 (a first drying step).

The main solvent of the sol is not limited, but it is preferred to use,for example, an ethanol-based solvent. In the present embodiment,2-n-butoxyethanol having a boiling point of 176° C. is used. In thepresent embodiment, therefore, the coated sol is heated at a temperaturelower than 176° C. as the boiling point of the solvent, for example, atabout 140° C., and held at this temperature for a time of the order of 3minutes in the first drying step to dry the piezoelectric precursor film71.

Then, the piezoelectric precursor film 71 is heated again to atemperature higher than that during the first drying step, for example,in the present embodiment, and held at this temperature for a certaintime to evaporate the main solvent of the sol further, thereby dryingthe piezoelectric precursor film 71 (a second drying step). Thetemperature reached in the second drying step is set at 140° C. to 170°C. The drying time is preferably of the order of 5 to 50 minutes.

A heating device used in such drying steps is, for example, a clean oven(diffusion furnace), or a baking device. The use of a baking device, inparticular, is preferred, because with the clean oven, the temperatureis controlled by applying hot air, so that the characteristics of thepiezoelectric precursor film tend to vary in the planar direction of thepassage-forming substrate wafer.

After the piezoelectric precursor film 71 is dried by theabove-mentioned first and second drying steps, the piezoelectricprecursor film 71 is degreased for a certain time at a certaintemperature in the air atmosphere (a degreasing step). Degreasing refersto releasing the organic components of the sol film, for example, asNO₂, CO₂ and H₂O.

The method of heating in the degreasing step is not limited, but in thepresent embodiment, the passage-forming substrate wafer is placed on ahot plate to raise the temperature of the piezoelectric precursor film71 to a predetermined temperature. In decreasing the rate of temperatureraising (i.e., the heating-up rate), the passage-forming substrate wafer110 is heated via a jig which is an aluminum plate having apredetermined thickness and having a slightly larger outer diameter thanthat of the wafer. The degreasing temperature in the degreasing step isset at a temperature in the range of 350° C. to 450° C. If thetemperature is too high, crystallization begins. If the temperature istoo low, the distribution of the Zr/Ti composition is wide. Thedegreasing step is preferably performed for 10 minutes or longer.

In order to improve the crystallinity of the piezoelectric layer, theheating-up rate in the degreasing step is important. Concretely, theheating-up rate in the degreasing step is set at 15 [° C./sec] orhigher. By so doing, the (100) orientation intensity of thepiezoelectric layer can be increased, and the distribution of thecomposition ratio of the components other than lead which constitute thepiezoelectric layer, for example, the distribution of the Zr/Ticomposition, can be decreased.

The “heating-up rate” referred to herein is defined as follows: Heatingbegins when the temperature is room temperature, and ends when a certaintemperature is reached. The rate of change in temperature over time isdetermined based on a period from a time when the temperature rises fromroom temperature by 20% of the temperature difference between roomtemperature and the temperature reached, until a time when thetemperature becomes 80% of the temperature difference. For example,assume that the temperature is raised from room temperature (25° C.) to100° C. over the course of 50 seconds. The heating-up rate in this caseis (100−25)×(0.8−0.2)/50=0.9 [° C./sec].

The coating step, the first drying step, the second drying step, and thedegreasing step described above are repeated a predetermined number oftimes, for example, twice in the present embodiment. As a result, thepiezoelectric precursor film 72 of a predetermined thickness is formed,as shown in FIG. 4B. In the present embodiment, the coating step, thefirst drying step, the second drying step, and the degreasing step arerepeated twice to form the piezoelectric precursor film 72 of apredetermined thickness. However, it goes without saying that the numberof repeats is not limited to 2, but may be one or three or more.

Then, the piezoelectric precursor film 72 of a predetermined thicknessis heat-treated for crystallization to form the piezoelectric film 73 (afiring step). The firing conditions differ according to the material. Inthe present embodiment, for example, the piezoelectric precursor film 72is fired by heating at 680° C. or above for 5 to 30 minutes, whereby thepiezoelectric film 73 is formed. An RTA (rapid thermal annealing) deviceis used as the heating device, and the heating-up rate in the firingstep is set at 100 [° C./sec] to 150 [° C./sec] to perform rapidheating. Since the heating-up rate is set at 100 [° C./sec] to 150 [°C./sec] for rapid heating, foreign matter in the film is decreased.

The coating step, the first and second drying steps, the degreasingstep, and the firing step described above are repeated a plural numberof times, whereby the piezoelectric layer 70 of a predeterminedthickness consisting of a plurality of (5 in the present embodiment) thepiezoelectric films 73 is formed, as shown in FIG. 4C. If the filmthickness per coating of the sol is of the order of 0.1 μm, for example,the total film thickness of the piezoelectric layer 70 is about 1 μm.

The composition of the sol coated in the coating step will be describedbelow.

The composition of the sol needs to be one such as to optimize theamount of displacement and durability, namely, the displacement decreaserate, of the piezoelectric layer 70. In the present embodiment, the solhaving the Pb:Zr:Ti composition represented by 1.18:0.51-0.52:0.48-0.49is used in order to form the piezoelectric layer 70 comprising leadzirconate titanate (PZT). By using the sol having this composition, asufficient amount of displacement for ink ejection can be ensured, andthe decrease rate of displacement upon repeated displacement can be keptminimal.

A pulse durability test was conducted on an actuator using the solhaving the Pb:Zr:Ti composition ratio of 1.18:0.51-0.52:0.48-0.49. Forexample, durability was examined when the initial displacement was 360nm, and a pulse of 35V was applied repeatedly. It was confirmed thateven upon application of 10,000 million pulses, an amount ofdisplacement of 320 nm posing no problem in practical use could beensured.

Durability was also examined when the initial displacement was 400 nm,and a pulse of 35V was applied repeatedly with the use of the sol havingthe Pb:Zr:Ti composition ratio of 1.18:0.46:0.54. Upon application ofless than 10,000 million pulses, the amount of displacement decreased to320 nm or smaller. However, no harm is done to durability at aboutseveral hundred million pulses to 3,000 million pulses, the appliedpulse number for a liquid-jet apparatus used in ordinary households.

The results of investigation into the relationship between the amount ofPb and the decrease rate of displacement are described based on FIG. 17which is a graph illustrating this relationship. The decrease rate ofdisplacement is desired to be 10% or less from the point of view ofreliability. The status of a decrease in displacement was tested, withthe ratio of Pb to (Zr/Ti) being changed. As shown in FIG. 17, theminimum value of the displacement decrease rate (%) exists (littledecrease in displacement occurs) when the ratio of Pb is between 1.14and 1.21. At the Pb ratio of 1.18, the displacement decrease rate takesthe minimum value less than 5%. Thus, the composition ratio ofPb:(Zr/Ti) is found to be preferably set at (1.10-1.20):1.00, especially1.18:1.00. Based on these results, the ratio of Pb:(Zr/Ti) is set at1.18:1.00 in the present embodiment. The composition ratio of Pb:(Zr/Ti)can be set in the range of (1.10-1.20):1.00.

Next, the relationship between the Zr/Ti ratio and the displacementdecrease rate will be described. The displacement decrease rate versusthe Zr/Ti ratio is also desired to be 10% or less from the viewpoint ofreliability. When the Zr/Ti ratio was (0.46-0.51)/(0.54-0.49), theamount of initial displacement was 360 nm or more, and the displacementdecrease rate was 10% or less.

Based on these results, in the present embodiment, the composition ratioof Pb:(Zr/Ti) can be set at 1.18:1.00, and the composition ratio ofZr:Ti can be set in the range of (0.46-0.51):(0.54-0.49).

The relationship between the Zr/Ti ratio and the distortion factor willbe described. The distortion factor refers to a value obtained bysubtracting the length (l) of an object in zero electric field from thelength (l′) of the object extended upon application of a predeterminedelectric field, and dividing the resulting difference (Δl) by 1. Agreater distortion factor means a larger amount of initial displacement.The distortion factor at 230 kV/cm (film thickness 1.1 μm 23V) took thehighest value at Zr/Ti in the vicinity of 51-52/48-49. The amount ofinitial displacement was about 400 nm. The displacement decrease rate atthe Zr/Ti ratio of 51-52/48-49 can be kept down to 5% or less.

Based on the above results, the use of the sol having the Pb:Zr:Ticomposition ratio of 1.18:(0.51-0.52):(0.48-0.49) makes it possible toachieve the curtailment of the displacement decrease rate and theensuring of a high amount of initial displacement.

As described above, the method of producing the dielectric film(piezoelectric layer 70) of the present embodiment includes the coatingstep of coating a colloidal solution containing an organometalliccompound containing a metal constituting a dielectric film containing atleast a lead component to form a dielectric precursor film, the dryingstep of drying the dielectric precursor film, the degreasing step ofdegreasing the dielectric precursor film, and the firing step of firingthe dielectric precursor film to form a dielectric film, and wherein thedrying step includes the first drying step of heating the dielectricprecursor film at a temperature lower than the boiling point of asolvent, which is a main solvent of the above-mentioned material, andholding the dielectric precursor film at this temperature for a certainperiod of time to dry the dielectric precursor film, and the seconddrying step of drying the dielectric precursor film at a temperature inthe range of 140° C. to 170° C., the degreasing step is performed at adegreasing temperature of 350° C. to 450° C. and at a heating-up rate of15 [° C./sec] or higher, and the firing step is performed at aheating-up rate of 100 [° C./sec] to 150 [° C./sec].

The drying step and the degreasing step narrow the distribution of theZr/Ti composition, and the firing step decreases foreign matter, so thatthe crystals of the dielectric film grow satisfactorily, and thedielectric film in the desired crystalline state can be formed. That is,a PZT film having Zr/Ti at the B site uniformly distributed therein isobtained. Here, if the composition of the piezoelectric layer having thelead component is expressed as ABOx, lead is indicated at the A site,and components other than the component at the A site are indicated atthe B site.

According to the drying step and the degreasing step, the distributionof the Zr/Ti composition in the film thickness direction is renderedless than 3% when expressed as a value in the Zr/Ti composition gradientanalyzed by ESCA. By so doing, a PZT film having Zr/Ti uniformlydistributed therein is obtained. In the firing step, the dielectricprecursor film is heated by the RTA method. The RTA method can rapidlyheat the dielectric precursor film at 100 [° C./sec] to 150 [° C./sec]which is the desired heating-up rate. As a result, the crystals can bepreferred-oriented in the (100) plane of a rhombohedral system, and adielectric film having excellent mechanical characteristics can beformed.

Hence, the present invention provides a method for producing adielectric film whose crystalline state is controlled relatively easilyto obtain constantly stable characteristics.

The following is an explanation for setting of the conditions for dryingat a temperature of 140° C. to 170° C. which are the temperatureconditions for the second drying step; the conditions for degreasing at350° C. to 450° C. and degreasing at a heating-up rate of 15 [° C./sec]or higher, which are the temperature conditions for the degreasing step;the conditions for firing at 100 [° C./sec] to 150 [° C./sec] which isthe heating-up rate for the firing step.

The ideal shape of PZT is such that the directions of polarizations inany regions should make the same angle with respect to the electricfield, and these directions should be different from the direction ofthe electric field (namely, the entire film has to fulfill thedefinition of the engineered domain). For this purpose, the followingrequirements need to be fulfilled.

I. The composition ratio of Zr/Ti should be uniform in the entire film,because the crystal system and the direction of polarization differaccording to the Zr/Ti ratio.

(i) Analysis by ESCA . . . According to ESCA (electron spectroscopy ofchemical analysis), the energy distribution of photoelectrons releasedupon X-ray irradiation of the surface of a sample is measured to giveknowledge of the composition of the sample. Since the analysis of notonly the outermost surface, but also regions in the depth direction canbe made by etching with Ar ions, the Zr/Ti distribution in the filmthickness direction can be investigated.

(ii) Measurement by XRD . . . The lattice constant of PZT crystalsdepends on the Zr/Ti composition ratio. Since the lattice constant isgreater on the Zr-rich side, XRD peaks appear on the low-angle side. Ifvariations in the Zr/Ti distribution are great within the PZT film (thefilm is divided into a Zr-rich region and a Ti-rich region), the latticeconstant of PZT is distributed somewhat widely, so that the half-widthof the diffraction peak of PZT is broad. The present embodiment targetsa uniform distribution of Zr/Ti, and thus prefers a narrow PZT (100)diffraction peak.

II. The film should be completely crystalline and free from phases.Observation of a section of the film based on its TEM image or SEM imagemay show foreign matter within the film. In this case, the foreignmatter is assumed to be low-density layers or vacancies. Such a film isnot the desired completely crystalline film, and the foreign matter doesnot contribute to piezoelectric characteristics, but deteriorates thepiezoelectric characteristics.

The heat treatment conditions for the PZT sol that fulfill the aboverequirements I and II were investigated. Brief outlines of the steps areas follows:

a. Coating of sol

b. Drying step 1: 140° C., 3 min

c. Drying step 2

d. Degreasing step

e. Firing step (crystallization of sol)

1. Conditions for the Degreasing Step

The dependence of the Zr/Ti distribution and the amount of foreignmatter on the degreasing conditions was investigated. Matrices ((1) to(4)) representing the relationship between the heating-up rate and thetemperature, as shown in FIG. 5, were constructed, as samples, to lookinto differences in the Zr/Ti distribution and the amount of foreignmatter according to the temperature and heating-up rate of degreasing.The temperatures reached were 320° C. and 400° C., and the heating-uprate was adjusted according the presence or absence of a degreasing jig.(The conditions for the first drying step and the conditions for thesecond drying step were 140° C., 3 minutes, and 170° C., 20 minutes,respectively, while the conditions for the firing step were fixed at700° C., 30 minutes in a diffusion furnace.)

The Zr/Ti composition gradient due to nonuniform distribution of Zr/Tiwas examined by ESCA. The sample (1) corresponded to the presence of thejig at 320° C., and the sample (3) corresponded to direct placement,without the jig, at 400° C. The results are shown in FIGS. 6A and 6B,which represent concentration distributions in the depth direction(depth profiles) obtained with the samples (1) and (3). FIG. 6A offersthe results with the sample (1), showing that variations occurred in theconcentrations of titanium (Ti) and zirconium (Zr), in the depthdirection of the piezoelectric layer, of the PZT components constitutingthe piezoelectric element. FIG. 6B offers the results with the sample(3), showing that variations, in the depth direction of thepiezoelectric layer, in the concentrations of the PZT componentsconstituting the piezoelectric element were smaller than those of thesample (1), namely, that the composition gradient was greater in thesample (1).

The composition gradient was defined in the following manner for itsquantitative evaluation: Attention was paid to Zr in the ESCA depthprofile, and the moving averages of its intensity data were taken at 5time points. The maximum value (Max) and the minimum value (Min) of themeasured intensity were described from the measured numerical data onthe PZT layer. The composition gradient was expressed as(Max−Min)/(Max+Min). The higher the value of the quotient obtained, thegreater the composition gradient.

Of the respective samples, the sample (1) took the highest value of thecomposition gradient at 20%, and the sample (3) took the lowest value ofthe composition gradient at 9.7%, meaning an approximately two-folddifference. The values for the samples (2) and (4) were nearly the sameat 13%. These findings reveal that the composition gradient can bedecreased as the degreasing temperature increases and the heating-uprate increases.

The above results are clear from the half-width of the PZT (100) peak aswell. Under the conditions at which the composition gradient is greater,the half-width is larger. The results of the TEM observation of thephases in the PZT film are shown in FIGS. 7A and 7B. FIG. 7A is asectional TEM image of the sample (1) degreased at 320° C. with the useof the jig, and FIG. 7B is a sectional TEM image of the sample (3)degreased at 400° C. in the directly placed state. As shown in thedrawings, foreign matter was larger in size and higher in density inFIG. 7B, and was present in larger amounts, particularly, on theeven-numbered layers, where continuity of crystals was assumed to bepoor. In the samples (2) and (4), the amounts of foreign matter wereintermediate between those of the samples (1) and (3). Accordingly, itis seen that the amount of foreign matter is smaller at a lowerdegreasing temperature and at a lower heating-up rate.

The above results are summarized in tabular form in FIG. 8. This tableshows that the composition gradient and the amount of foreign matter arein a trade-off relation, and these parameters are incompatible with eachother, even if the degreasing conditions are adjusted.

2. Conditions for the Second Drying Step

Next, experiments were conducted, with the temperature of the seconddrying step being varied. To keep the composition gradient to a minimum,the conditions for the degreasing step were fixed at (3) 400°, directplacement. The dependence of the PZT (100) diffraction peak half-widthon the temperature of the second drying step was as shown in FIG. 9. Thecurve in FIG. 9 showed a peak at the temperature of the second dryingstep in the vicinity of 220° C. The half-width increased between 170° C.and 220° C., and decreased gently on a higher temperature side. Thehalf-width at a temperature of 350° C. to 400° C. was nearly the same asthat on the low temperature side.

Next, the influence of the temperature of the second drying step onforeign matter contained in the film will be mentioned. A comparisonwill be made between the absence of the second drying step giving asmall PZT (100) half-width (small composition gradient) and thetemperature of the second drying step being 220° which gives a largehalf-width (great composition gradient) (FIGS. 10A, 10B). FIG. 10A is asectional TEM image taken when there was no second drying step, whileFIG. 10B is a sectional TEM image taken when the temperature of thesecond drying step was 220° C.

It is noted that the amount of foreign matter was overwhelmingly largerin the situation of FIG. 10A than in the situation of FIG. 10B.Interlayer foreign matter was present, and tiny foreign matter existedin the layers as well. In some places, foreign matter was tied togetherin the direction of the film surface.

To sum up, it is understood that the temperature of the second dryingstep should be set at 170° C. or lower, or the second drying step shouldbe eliminated, in order to render the composition gradient small. Undersuch conditions, however, the amount of foreign matter increases. Thatis, the relation between the composition gradient and foreign matter isa trade-off as for the degreasing step. Even under the temperatureconditions of the second drying step, these two parameters areincompatible.

3. Conditions for the Firing Step

Rapid heating and firing by RTA is adopted. The composition gradient canbe reduced by the conditions of the second drying step and theconditions of the degreasing step. The problem of foreign matter issolved by markedly increasing the heating-up rate in the firing step. Toraise the heating-up rate markedly, rapid heating by RTA is performed inthe firing step.

The following is the results of experiments involving rapid heating andfiring by use of RTA. To decrease the composition gradient, thetemperature of the second drying step was fixed at 160° C., and thetemperature of the degreasing step was fixed at 400° C. in the directplacement state. FIG. 11A is a sectional TEM image of a sample heated upto 700° C. at 1 [° C./sec] which was lower than the heating-up rate of adiffusion furnace used in ordinary treatment (about 3 [° C./sec]). FIG.11B is a sectional TEM image of a sample heated at a heating-up rate of120 [° C./sec].

As shown in FIG. 11A, in the case of the sample heated up to 700° C. at1 [° C./sec], foreign matter was present almost throughout the sample toa worse degree than in FIG. 10A indicated earlier. With the sampleheated at a heating-up rate of 120 [° C./sec] (for example, when at 630°C.), on the other hand, it is seen that foreign matter was scanty. Therewas little foreign matter in the layers, and interlayer foreign matterwas in a markedly small amount.

FIG. 12 shows the distribution of concentration in the depth direction(depth profile) of the sample heated at a heating-up rate of 120 [°C./sec]. There were no variations, in the depth direction of thepiezoelectric layer, in the concentrations of the PZT componentsconstituting the piezoelectric element. That is, the compositiongradient of Zr/Ti was kept down. This means that foreign matter ismarkedly cut down, and the uniformity of the Zr/Ti distribution isimproved, by rapid heating using RTA in the firing step to carry outtreatment for 5 minutes at a heating-up rate of 120 [° C./sec].

4. Conclusion

Based on the above results, the heat treatment conditions are determinedas shown below, so that the Zr/Ti composition gradient can be renderedsmall by the first drying step, the second drying step, and thedegreasing step to distribute Zr/Ti uniformly, and foreign matter can becut down by the firing step.

First drying step: 140° C., 3 min.

Second drying step: 160° C., 5 min.

Degreasing step: Heating-up rate corresponding to 400° C., 5 min, directplacement on a hot plate.

Firing step: 5 min at heating-up rate at 100 [° C./sec] to 150 [°C./sec] (rapid heating by RTA)

The results of the improvements in the heat treatment conditions aretabulated in FIG. 13, and the XRD waveform of PZT as the piezoelectriclayer is shown in FIG. 14. FIG. 14 shows the (100) diffraction peak ofPZT.

As shown in FIG. 13, the PZT (100) diffraction intensity was 600 to1,000 cps before improvement, but increased to 1,050 to 1,350 cps afterimprovement. The PZT (100) peak half-width was 0.24° to 0.28° beforeimprovement, but decreased to 0.21° to 0.22° after improvement. TheZr/Ti composition gradient by ESCA was 10% or greater beforeimprovement, but decreased to 1.1% (less than 3%) after improvement, andforeign matter in the film was large in amount before improvement, butchanged to a very small amount after improvement.

Hence, the distribution of the Zr/Ti composition is rendered small, andforeign matter is decreased so that crystals of the dielectric film(piezoelectric layer 70) can be grown satisfactorily, and the dielectricfilm in the desired crystalline state can be formed. That is, a PZT filmhaving Zr/Ti at the B site uniformly distributed therein is obtained.That is, it is possible to obtain a PZT film (piezoelectric layer 70)having a high PZT (100) diffraction intensity, a small PZT (100)diffraction peak half-width, a satisfactorily uniform distribution ofthe Zr/Ti composition in the film, and few phases contained in the film,and thus improve piezoelectric characteristics.

After formation of the piezoelectric layer 70 in the aforementionedmanner, the upper electrode film 80 comprising, for example, iridium(Ir) is formed on the entire surface of the passage-forming substratewafer 110, as shown in FIG. 15A. Then, the piezoelectric layer 70 andthe upper electrode film 80 are patterned in a region corresponding toeach pressure generating chamber 12 to form a piezoelectric element 300,as shown in FIG. 15B. Then, the lead electrode 90 is formed. Concretely,a metal layer 91 comprising, for example, gold (Au) is formed on theentire surface of the passage-forming substrate wafer 110, as shown inFIG. 15C. Then, the metal layer 91 is patterned for each piezoelectricelement 300 via a mask pattern (not shown) comprising, for example, aresist, whereby the lead electrode 90 is formed.

Then, as shown in FIG. 15D, a protective plate wafer 130, which is asilicon wafer and becomes a plurality of protective plates, is joined toa side of the passage-forming substrate wafer 110 where thepiezoelectric elements 300 have been formed. The protective plate wafer130 has a thickness, for example, of the order of 400 μm, and thus, therigidity of the passage-forming substrate wafer 110 is markedlyincreased by joining the protective plate wafer 130.

Then, as shown in FIG. 16A, the passage-forming substrate wafer 110 ispolished to a certain thickness, and then wet etched with fluoronitricacid to impart a predetermined thickness to the passage-formingsubstrate wafer 110. In the present embodiment, for example, thepassage-forming substrate wafer 110 is etched to have a thickness ofabout 70 μm. Then, as shown in FIG. 16B, a mask film 52 comprising, forexample, silicon nitride (SiN) is newly formed on the passage-formingsubstrate wafer 110, and patterned into a predetermined shape. Thepassage-forming substrate wafer 110 is anisotropically etched via themask film 52 to form the pressure generating chambers 12, thecommunicating portion 13, and the ink supply paths 14 in thepassage-forming substrate wafer 110, as shown in FIG. 16C.

Then, unnecessary portions of the outer peripheral edge portions of thepassage-forming substrate wafer 110 and the protective plate wafer 130are removed by cutting using, for example, dicing. Then, the nozzleplate 20 having the nozzle orifices 21 bored therein is joined to asurface of the passage-forming substrate wafer 110 on the side oppositeto the protective plate wafer 130, and the compliance plate 40 is joinedto the protective plate wafer 130. Further, the passage-formingsubstrate wafer 110, etc. are divided into the passage-formingsubstrates 10, each of a single chip size, as shown in FIG. 1, therebypreparing the ink-jet recording head of the present embodiment.

Thus, the resulting ink-jet recording head can be a liquid-jet headfurnished with the piezoelectric elements 300 each having thepiezoelectric layer 70 comprising the dielectric film in the desiredcrystalline state.

OTHER EMBODIMENTS

The embodiments of the present invention have been described above, butthe present invention is not limited to these embodiments. In theabove-described embodiments, the ink-jet recording head is taken as anexample for illustrating the present invention. However, the presentinvention can be applied to heads for jetting liquids other than ink.Other liquid-jet heads include, for example, various recording heads foruse in image recording devices such as printers, color material jetheads for use in the production of color filters for liquid crystaldisplays, electrode material jet heads for use in the formation ofelectrodes for organic EL displays and FED (face emitting displays), andbio-organic material jet heads for use in the production of biochips.

Furthermore, the present invention is not limited to the method forproducing the liquid-jet head having the piezoelectric elements. Thatis, the present invention is not limited to the method for producing thepiezoelectric layer comprising the piezoelectric material, but needlessto say, can be applied to the production of dielectric films comprisingevery dielectric material. It should be understood that such changes,substitutions and alterations can be made therein without departing fromthe spirit and scope of the invention as defined by the appended claims.

1. A method for producing a dielectric film, comprising: a coating stepof coating a colloidal solution containing an organometallic compoundcontaining a metal constituting a dielectric film containing at least alead component to form a dielectric precursor film; a drying step ofdrying the dielectric precursor film; a degreasing step of degreasingthe dielectric precursor film; and a firing step of firing thedielectric precursor film to form a dielectric film, and wherein thedrying step includes a first drying step of heating the dielectricprecursor film to a temperature lower than a boiling point of a solvent,which is a main solvent of the material, and holding the dielectricprecursor film at the temperature for a certain period of time to drythe dielectric precursor film, and a second drying step of drying thedielectric precursor film at a temperature in a range of 140° C. to 170°C., the degreasing step is performed at a degreasing temperature of 350°C. to 450° C. and at a heating-up rate of 15 [° C/sec] or higher, andthe firing step is performed at a heating-up rate of 100 [° C/sec] to150 [° C/sec], wherein the dielectric film containing at least the leadcomponent is lead zirconate titanate (PZT), and a distribution of aZr/Ti composition in a film thickness direction is rendered less than3%, when expressed as a value of a Zr/Ti composition gradient analyzedby ESCA, by the drying step, the degreasing step, and the firing step.2. The method for producing a dielectric film according to claim 1,wherein in the firing step, the dielectric precursor film is heated byan RTA method.
 3. The method for producing a dielectric film accordingto claim 1, wherein crystals are preferred-oriented in a (100) plane ofa rhombohedral system.
 4. A method for producing a piezoelectricelement, comprising the steps of: forming a lower electrode film on asubstrate; forming a piezoelectric layer on the lower electrode film;and forming an upper electrode film on the piezoelectric layer, andwherein the step of forming the piezoelectric layer is a method forproducing the dielectric film produced by the producing method accordingto claim
 1. 5. A method for producing a liquid-jet head, using thepiezoelectric element produced by the producing method according toclaim 4.